It is normal for a baby to suck. This is how he relaxes and feeds. The closer your child is when they are 2 or 3 years old, the less they need to suck. If this is not the case, the use of a pacifier is recommended rather than thumb sucking.
Why? Because YOU can control when and how your child uses a pacifier, but not his thumb. Never put sugar, honey or corn syrup on a lollipop. This may cause cavities. It is best if your child stops sucking BEFORE 3 years old. If a child continues to suck his thumb or lollipop AFTER his permanent teeth have appeared, the growth of his jaw and the position of his teeth could be affected.